The present disclosure relates generally to power transmission systems. Alternating current (AC) power lines are commonly used in bulk power transmission. As the number of customers connected to the power transmission system increases, power demand will exceed the capabilities of existing AC power lines. One way to increase power line capability is to convert an existing AC power line to a direct current (DC) power line. Increasing power line capability is particularly important in areas where installing additional power lines are costly and time consuming, such as urban areas. Existing methods and systems for converting power transmission systems to DC power lines suffer from a number of shortcomings and disadvantages. There remain unmet needs including increasing transmission line longevity, reducing working stress, reducing operating costs, reducing power losses, and increasing reliability. For instance, a DC power line constantly transmitting power at a high voltage is subject to high working stress, reducing line longevity. There is a significant need for the unique apparatuses, methods, systems and techniques disclosed herein.